The invention concerns a method for the vitrification of waste materials, and more particularly for waste materials which contain high quantities of carbon, in an electrically heated glass melting furnace, whereby the waste gases from the glass melting furnace are subjected to secondary combustion.
Methods of this type are already known, whereby according to U.S. Pat. No. 4,944,785, owned by the assignee of the present application, dust and sludge produced by waste gas cleaning during the vitrification of waste materials are returned to the process by being mixed into the batch.
This method may result in problems with the recycling of the dust and sludge if the waste material which is to be vitrified contains large amounts of carbon. When ashes with a high carbon content are melted, a fluid layer can be formed on the surface of the electrically heated glass melt, which results in a high level of dust emission with the waste gases.
In addition, the apparatus used to carry out the method is not suitable for continuous, trouble-free operation and it is difficult to use all the energy from the waste gases, and to achieve complete cleaning thereof.
The German published application DE-OS 38 41 889 describes a method of converting solid, virtually water-free waste materials into glass, whereby the waste materials are mixed with one or more additional materials to form a batch to be melted, whereby the main part of the batch is melted to glass by the application of heat, and a small part is led off in the form of waste gases emitted from the melting batch, whereby solid glass bodies are produced from the glass melt by casting and cooling, whereby ash from the incineration of refuse is used as the waste product, whereby the hot waste gases are drawn off without contact with the surrounding air and are returned to the batch and cooled to a temperature between 20.degree. C. and 50.degree. C., whereby the condensation products formed during cooling are melted with the batch and whereby the cold waste gases which emanate from the batch are subjected to one of the state of the art waste gas cleaning processes.
The apparatus for carrying out the method according to German published application DE-OS 38 41 889 is characterized by an enclosed batch mixer with an inlet for solid materials through which the ash from waste incineration and the additional materials are fed for mixing, with an outlet for the finished batch which is ready for melting, and with a gas inlet and gas outlet, by an enclosed glass melting furnace with a batch charger at one end of the furnace, which is connected to the solid material outlet of the batch mixer, with at least one waste gas flue opening, and with an outlet for the molten glass at the other end of the furnace, and by a gas cleaning device, the entry of which is connected to the gas outlet of the batch mixer.
A disadvantage of this method, and the disclosed apparatus, is that it is not suitable for waste materials which contain large amounts of carbon, as no afterburning is provided, and as the waste gas energy is not fully exploited.